Diagnosis Method for Thermal Aging and Water Tree Aging of Insulation Based on Lissajous Figure and Current Harmonic Characteristic Quantity

Power cables are one of the most important devices in the power system. In order to diagnose the aging state of XLPE cable insulation, this paper carried out 90°C, 120°C, 150°C accelerated thermal aging experiments and accelerated water tree aging experiments on the cable section samples in the laboratory, tested and analyzed the changing laws of $\tan\delta-f$ curves, Lissajous figures and current harmonic content of different samples. The experimental results show that for the cable section samples with internal water tree aging, the Lissajous figure inclination angle is significantly larger than that of the thermal aging samples, and the harmonic component of the current is mainly within tenth order. With the increase of aging time, the characteristics will be more obvious, so the ageing type of the cable can be distinguished. At the same time, the minor axis length of the Lissajous figure and the harmonic distortion within the tenth order THD10 have a good correlation with the $\tan\delta$ of the cable, which can be used to judge the aging degree of the cable.